std::ranges::subrange
Defined in header <ranges> | ||
|---|---|---|
template<
std::input_or_output_iterator I,
std::sentinel_for<I> S = I,
ranges::subrange_kind K = std::sized_sentinel_for<S, I> ?
ranges::subrange_kind::sized :
ranges::subrange_kind::unsized >
requires (K == ranges::subrange_kind::sized || !std::sized_sentinel_for<S, I>)
class subrange
: public ranges::view_interface<subrange<I, S, K>>
| (1) | (since C++20) |
| Helper concepts | ||
template<class From, class To>
concept /*uses-nonqualification-pointer-conversion*/ =
/* see description */;
| (2) | (exposition only*) |
template<class From, class To> concept /*convertible-to-non-slicing*/ = /* see description */; | (3) | (exposition only*) |
1) The
subrange class template combines together an iterator and a sentinel into a single view. It models sized_range whenever the final template parameter is subrange_kind::sized (which happens when std::sized_sentinel_for<S, I> is satisfied or when size is passed explicitly as a constructor argument).
2) Determines whether
From is convertible to To without qualification conversions. Equivalent to: template<class From, class To>
concept /*uses-nonqualification-pointer-conversion*/ =
std::is_pointer_v<From> && std::is_pointer_v<To> &&
!std::convertible_to<std::remove_pointer_t<From>(*)[],
std::remove_pointer_t<To>(*)[]>;
3) Determines whether
From is convertible to To without derived-to-base conversion: template<class From, class To>
concept /*convertible-to-non-slicing*/ =
std::convertible_to<From, To> &&
!/*uses-nonqualification-pointer-conversion*/
<std::decay_t<From>, std::decay_t<To>>;
Data members
| Member | Description |
|---|---|
constexprbool StoreSize [static] |
K == ranges::subrange_kind::sized && !std::sized_sentinel_for<S, I>(exposition-only static member constant*) |
I begin_ | an iterator to the beginning of the subrange (exposition-only member object*) |
S end_ | a sentinel denoting the end of the subrange (exposition-only member object*) |
make-unsigned-like-t <std::iter_difference_t<I>> size_ (present only if StoreSize is true) | the size of the subrange (exposition-only member object*) |
Member functions
creates a new subrange (public member function) |
|
converts the subrange to a pair-like type (public member function) |
|
Observers |
|
| obtains the iterator (public member function) |
|
| obtains the sentinel (public member function) |
|
checks whether the subrange is empty (public member function) |
|
obtains the size of the subrange (public member function) |
|
Iterator operations |
|
| advances the iterator by given distance (public member function) |
|
obtains a copy of the subrange with its iterator decremented by a given distance (public member function) |
|
obtains a copy of the subrange with its iterator advanced by a given distance (public member function) |
|
Inherited from |
|
|
(C++23) | returns a constant iterator to the beginning of the range (public member function of std::ranges::view_interface<D>) |
|
(C++23) | returns a sentinel for the constant iterator of the range (public member function of std::ranges::view_interface<D>) |
returns whether the derived view is not empty, provided only if ranges::empty is applicable to it (public member function of std::ranges::view_interface<D>) |
|
gets the address of derived view's data, provided only if its iterator type satisfies contiguous_iterator (public member function of std::ranges::view_interface<D>) |
|
returns the first element in the derived view, provided if it satisfies forward_range (public member function of std::ranges::view_interface<D>) |
|
returns the last element in the derived view, provided only if it satisfies bidirectional_range and common_range (public member function of std::ranges::view_interface<D>) |
|
returns the nth element in the derived view, provided only if it satisfies random_access_range (public member function of std::ranges::view_interface<D>) |
|
Deduction guides
Non-member functions
|
(C++20) | obtains iterator or sentinel from a std::ranges::subrange (function template) |
Helper types
|
(C++20) | specifies whether a std::ranges::subrange models std::ranges::sized_range (enum) |
|
(C++20) | obtains the size of a std::ranges::subrange (class template specialization) |
|
(C++20) | obtains the type of the iterator or the sentinel of a std::ranges::subrange (class template specialization) |
Helper templates
template< class I, class S, ranges::subrange_kind K > constexpr bool ranges::enable_borrowed_range<ranges::subrange<I, S, K>> = true; | (since C++20) |
This specialization of ranges::enable_borrowed_range makes subrange satisfy borrowed_range.
Example
#include <map>
#include <print>
#include <ranges>
void make_uppercase(char& v)
{
v += 'A' - 'a';
}
void uppercase_transform(std::multimap<int, char>& m, int k)
{
auto [first, last] = m.equal_range(k);
for (auto& [_, v] : std::ranges::subrange(first, last))
make_uppercase(v);
}
int main()
{
std::multimap<int, char> mm{{4, 'a'}, {3, '-'}, {4, 'b'}, {5, '-'}, {4, 'c'}};
std::println("Before: {}", mm);
uppercase_transform(mm, 4);
std::println("After: {}", mm);
}
Output:
Before: {3: '-', 4: 'a', 4: 'b', 4: 'c', 5: '-'}
After: {3: '-', 4: 'A', 4: 'B', 4: 'C', 5: '-'}
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3470 | C++20 |
convertible-to-non-slicing might reject qualification conversions | always accepts them |
See also
|
(C++20) | helper class template for defining a view, using the curiously recurring template pattern (class template) |
External links
Read/write all values of a std::multimap with a given key in C++20 — SO |
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